diff options
Diffstat (limited to 'block/blk-flush.c')
| -rw-r--r-- | block/blk-flush.c | 618 |
1 files changed, 618 insertions, 0 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c new file mode 100644 index 000000000..dc71da0e6 --- /dev/null +++ b/block/blk-flush.c @@ -0,0 +1,618 @@ +/* + * Functions to sequence PREFLUSH and FUA writes. + * + * Copyright (C) 2011 Max Planck Institute for Gravitational Physics + * Copyright (C) 2011 Tejun Heo <tj@kernel.org> + * + * This file is released under the GPLv2. + * + * REQ_{PREFLUSH|FUA} requests are decomposed to sequences consisted of three + * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request + * properties and hardware capability. + * + * If a request doesn't have data, only REQ_PREFLUSH makes sense, which + * indicates a simple flush request. If there is data, REQ_PREFLUSH indicates + * that the device cache should be flushed before the data is executed, and + * REQ_FUA means that the data must be on non-volatile media on request + * completion. + * + * If the device doesn't have writeback cache, PREFLUSH and FUA don't make any + * difference. The requests are either completed immediately if there's no data + * or executed as normal requests otherwise. + * + * If the device has writeback cache and supports FUA, REQ_PREFLUSH is + * translated to PREFLUSH but REQ_FUA is passed down directly with DATA. + * + * If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH + * is translated to PREFLUSH and REQ_FUA to POSTFLUSH. + * + * The actual execution of flush is double buffered. Whenever a request + * needs to execute PRE or POSTFLUSH, it queues at + * fq->flush_queue[fq->flush_pending_idx]. Once certain criteria are met, a + * REQ_OP_FLUSH is issued and the pending_idx is toggled. When the flush + * completes, all the requests which were pending are proceeded to the next + * step. This allows arbitrary merging of different types of PREFLUSH/FUA + * requests. + * + * Currently, the following conditions are used to determine when to issue + * flush. + * + * C1. At any given time, only one flush shall be in progress. This makes + * double buffering sufficient. + * + * C2. Flush is deferred if any request is executing DATA of its sequence. + * This avoids issuing separate POSTFLUSHes for requests which shared + * PREFLUSH. + * + * C3. The second condition is ignored if there is a request which has + * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid + * starvation in the unlikely case where there are continuous stream of + * FUA (without PREFLUSH) requests. + * + * For devices which support FUA, it isn't clear whether C2 (and thus C3) + * is beneficial. + * + * Note that a sequenced PREFLUSH/FUA request with DATA is completed twice. + * Once while executing DATA and again after the whole sequence is + * complete. The first completion updates the contained bio but doesn't + * finish it so that the bio submitter is notified only after the whole + * sequence is complete. This is implemented by testing RQF_FLUSH_SEQ in + * req_bio_endio(). + * + * The above peculiarity requires that each PREFLUSH/FUA request has only one + * bio attached to it, which is guaranteed as they aren't allowed to be + * merged in the usual way. + */ + +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/bio.h> +#include <linux/blkdev.h> +#include <linux/gfp.h> +#include <linux/blk-mq.h> + +#include "blk.h" +#include "blk-mq.h" +#include "blk-mq-tag.h" +#include "blk-mq-sched.h" + +/* PREFLUSH/FUA sequences */ +enum { + REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */ + REQ_FSEQ_DATA = (1 << 1), /* data write in progress */ + REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */ + REQ_FSEQ_DONE = (1 << 3), + + REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA | + REQ_FSEQ_POSTFLUSH, + + /* + * If flush has been pending longer than the following timeout, + * it's issued even if flush_data requests are still in flight. + */ + FLUSH_PENDING_TIMEOUT = 5 * HZ, +}; + +static bool blk_kick_flush(struct request_queue *q, + struct blk_flush_queue *fq, unsigned int flags); + +static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq) +{ + unsigned int policy = 0; + + if (blk_rq_sectors(rq)) + policy |= REQ_FSEQ_DATA; + + if (fflags & (1UL << QUEUE_FLAG_WC)) { + if (rq->cmd_flags & REQ_PREFLUSH) + policy |= REQ_FSEQ_PREFLUSH; + if (!(fflags & (1UL << QUEUE_FLAG_FUA)) && + (rq->cmd_flags & REQ_FUA)) + policy |= REQ_FSEQ_POSTFLUSH; + } + return policy; +} + +static unsigned int blk_flush_cur_seq(struct request *rq) +{ + return 1 << ffz(rq->flush.seq); +} + +static void blk_flush_restore_request(struct request *rq) +{ + /* + * After flush data completion, @rq->bio is %NULL but we need to + * complete the bio again. @rq->biotail is guaranteed to equal the + * original @rq->bio. Restore it. + */ + rq->bio = rq->biotail; + + /* make @rq a normal request */ + rq->rq_flags &= ~RQF_FLUSH_SEQ; + rq->end_io = rq->flush.saved_end_io; +} + +static bool blk_flush_queue_rq(struct request *rq, bool add_front) +{ + if (rq->q->mq_ops) { + blk_mq_add_to_requeue_list(rq, add_front, true); + return false; + } else { + if (add_front) + list_add(&rq->queuelist, &rq->q->queue_head); + else + list_add_tail(&rq->queuelist, &rq->q->queue_head); + return true; + } +} + +/** + * blk_flush_complete_seq - complete flush sequence + * @rq: PREFLUSH/FUA request being sequenced + * @fq: flush queue + * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero) + * @error: whether an error occurred + * + * @rq just completed @seq part of its flush sequence, record the + * completion and trigger the next step. + * + * CONTEXT: + * spin_lock_irq(q->queue_lock or fq->mq_flush_lock) + * + * RETURNS: + * %true if requests were added to the dispatch queue, %false otherwise. + */ +static bool blk_flush_complete_seq(struct request *rq, + struct blk_flush_queue *fq, + unsigned int seq, blk_status_t error) +{ + struct request_queue *q = rq->q; + struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx]; + bool queued = false, kicked; + unsigned int cmd_flags; + + BUG_ON(rq->flush.seq & seq); + rq->flush.seq |= seq; + cmd_flags = rq->cmd_flags; + + if (likely(!error)) + seq = blk_flush_cur_seq(rq); + else + seq = REQ_FSEQ_DONE; + + switch (seq) { + case REQ_FSEQ_PREFLUSH: + case REQ_FSEQ_POSTFLUSH: + /* queue for flush */ + if (list_empty(pending)) + fq->flush_pending_since = jiffies; + list_move_tail(&rq->flush.list, pending); + break; + + case REQ_FSEQ_DATA: + list_move_tail(&rq->flush.list, &fq->flush_data_in_flight); + queued = blk_flush_queue_rq(rq, true); + break; + + case REQ_FSEQ_DONE: + /* + * @rq was previously adjusted by blk_flush_issue() for + * flush sequencing and may already have gone through the + * flush data request completion path. Restore @rq for + * normal completion and end it. + */ + BUG_ON(!list_empty(&rq->queuelist)); + list_del_init(&rq->flush.list); + blk_flush_restore_request(rq); + if (q->mq_ops) + blk_mq_end_request(rq, error); + else + __blk_end_request_all(rq, error); + break; + + default: + BUG(); + } + + kicked = blk_kick_flush(q, fq, cmd_flags); + return kicked | queued; +} + +static void flush_end_io(struct request *flush_rq, blk_status_t error) +{ + struct request_queue *q = flush_rq->q; + struct list_head *running; + bool queued = false; + struct request *rq, *n; + unsigned long flags = 0; + struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx); + + if (q->mq_ops) { + struct blk_mq_hw_ctx *hctx; + + /* release the tag's ownership to the req cloned from */ + spin_lock_irqsave(&fq->mq_flush_lock, flags); + + if (!refcount_dec_and_test(&flush_rq->ref)) { + fq->rq_status = error; + spin_unlock_irqrestore(&fq->mq_flush_lock, flags); + return; + } + + if (fq->rq_status != BLK_STS_OK) { + error = fq->rq_status; + fq->rq_status = BLK_STS_OK; + } + + hctx = blk_mq_map_queue(q, flush_rq->mq_ctx->cpu); + if (!q->elevator) { + blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq); + flush_rq->tag = -1; + } else { + blk_mq_put_driver_tag_hctx(hctx, flush_rq); + flush_rq->internal_tag = -1; + } + } + + running = &fq->flush_queue[fq->flush_running_idx]; + BUG_ON(fq->flush_pending_idx == fq->flush_running_idx); + + /* account completion of the flush request */ + fq->flush_running_idx ^= 1; + + if (!q->mq_ops) + elv_completed_request(q, flush_rq); + + /* and push the waiting requests to the next stage */ + list_for_each_entry_safe(rq, n, running, flush.list) { + unsigned int seq = blk_flush_cur_seq(rq); + + BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH); + queued |= blk_flush_complete_seq(rq, fq, seq, error); + } + + /* + * Kick the queue to avoid stall for two cases: + * 1. Moving a request silently to empty queue_head may stall the + * queue. + * 2. When flush request is running in non-queueable queue, the + * queue is hold. Restart the queue after flush request is finished + * to avoid stall. + * This function is called from request completion path and calling + * directly into request_fn may confuse the driver. Always use + * kblockd. + */ + if (queued || fq->flush_queue_delayed) { + WARN_ON(q->mq_ops); + blk_run_queue_async(q); + } + fq->flush_queue_delayed = 0; + if (q->mq_ops) + spin_unlock_irqrestore(&fq->mq_flush_lock, flags); +} + +/** + * blk_kick_flush - consider issuing flush request + * @q: request_queue being kicked + * @fq: flush queue + * @flags: cmd_flags of the original request + * + * Flush related states of @q have changed, consider issuing flush request. + * Please read the comment at the top of this file for more info. + * + * CONTEXT: + * spin_lock_irq(q->queue_lock or fq->mq_flush_lock) + * + * RETURNS: + * %true if flush was issued, %false otherwise. + */ +static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq, + unsigned int flags) +{ + struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx]; + struct request *first_rq = + list_first_entry(pending, struct request, flush.list); + struct request *flush_rq = fq->flush_rq; + + /* C1 described at the top of this file */ + if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending)) + return false; + + /* C2 and C3 + * + * For blk-mq + scheduling, we can risk having all driver tags + * assigned to empty flushes, and we deadlock if we are expecting + * other requests to make progress. Don't defer for that case. + */ + if (!list_empty(&fq->flush_data_in_flight) && + !(q->mq_ops && q->elevator) && + time_before(jiffies, + fq->flush_pending_since + FLUSH_PENDING_TIMEOUT)) + return false; + + /* + * Issue flush and toggle pending_idx. This makes pending_idx + * different from running_idx, which means flush is in flight. + */ + fq->flush_pending_idx ^= 1; + + blk_rq_init(q, flush_rq); + + /* + * In case of none scheduler, borrow tag from the first request + * since they can't be in flight at the same time. And acquire + * the tag's ownership for flush req. + * + * In case of IO scheduler, flush rq need to borrow scheduler tag + * just for cheating put/get driver tag. + */ + if (q->mq_ops) { + struct blk_mq_hw_ctx *hctx; + + flush_rq->mq_ctx = first_rq->mq_ctx; + + if (!q->elevator) { + fq->orig_rq = first_rq; + flush_rq->tag = first_rq->tag; + hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu); + blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq); + } else { + flush_rq->internal_tag = first_rq->internal_tag; + } + } + + flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH; + flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK); + flush_rq->rq_flags |= RQF_FLUSH_SEQ; + flush_rq->rq_disk = first_rq->rq_disk; + flush_rq->end_io = flush_end_io; + + return blk_flush_queue_rq(flush_rq, false); +} + +static void flush_data_end_io(struct request *rq, blk_status_t error) +{ + struct request_queue *q = rq->q; + struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL); + + lockdep_assert_held(q->queue_lock); + + /* + * Updating q->in_flight[] here for making this tag usable + * early. Because in blk_queue_start_tag(), + * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and + * reserve tags for sync I/O. + * + * More importantly this way can avoid the following I/O + * deadlock: + * + * - suppose there are 40 fua requests comming to flush queue + * and queue depth is 31 + * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc + * tag for async I/O any more + * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT + * and flush_data_end_io() is called + * - the other rqs still can't go ahead if not updating + * q->in_flight[BLK_RW_ASYNC] here, meantime these rqs + * are held in flush data queue and make no progress of + * handling post flush rq + * - only after the post flush rq is handled, all these rqs + * can be completed + */ + + elv_completed_request(q, rq); + + /* for avoiding double accounting */ + rq->rq_flags &= ~RQF_STARTED; + + /* + * After populating an empty queue, kick it to avoid stall. Read + * the comment in flush_end_io(). + */ + if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error)) + blk_run_queue_async(q); +} + +static void mq_flush_data_end_io(struct request *rq, blk_status_t error) +{ + struct request_queue *q = rq->q; + struct blk_mq_hw_ctx *hctx; + struct blk_mq_ctx *ctx = rq->mq_ctx; + unsigned long flags; + struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx); + + hctx = blk_mq_map_queue(q, ctx->cpu); + + if (q->elevator) { + WARN_ON(rq->tag < 0); + blk_mq_put_driver_tag_hctx(hctx, rq); + } + + /* + * After populating an empty queue, kick it to avoid stall. Read + * the comment in flush_end_io(). + */ + spin_lock_irqsave(&fq->mq_flush_lock, flags); + blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error); + spin_unlock_irqrestore(&fq->mq_flush_lock, flags); + + blk_mq_sched_restart(hctx); +} + +/** + * blk_insert_flush - insert a new PREFLUSH/FUA request + * @rq: request to insert + * + * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions. + * or __blk_mq_run_hw_queue() to dispatch request. + * @rq is being submitted. Analyze what needs to be done and put it on the + * right queue. + */ +void blk_insert_flush(struct request *rq) +{ + struct request_queue *q = rq->q; + unsigned long fflags = q->queue_flags; /* may change, cache */ + unsigned int policy = blk_flush_policy(fflags, rq); + struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx); + + if (!q->mq_ops) + lockdep_assert_held(q->queue_lock); + + /* + * @policy now records what operations need to be done. Adjust + * REQ_PREFLUSH and FUA for the driver. + */ + rq->cmd_flags &= ~REQ_PREFLUSH; + if (!(fflags & (1UL << QUEUE_FLAG_FUA))) + rq->cmd_flags &= ~REQ_FUA; + + /* + * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any + * of those flags, we have to set REQ_SYNC to avoid skewing + * the request accounting. + */ + rq->cmd_flags |= REQ_SYNC; + + /* + * An empty flush handed down from a stacking driver may + * translate into nothing if the underlying device does not + * advertise a write-back cache. In this case, simply + * complete the request. + */ + if (!policy) { + if (q->mq_ops) + blk_mq_end_request(rq, 0); + else + __blk_end_request(rq, 0, 0); + return; + } + + BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */ + + /* + * If there's data but flush is not necessary, the request can be + * processed directly without going through flush machinery. Queue + * for normal execution. + */ + if ((policy & REQ_FSEQ_DATA) && + !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) { + if (q->mq_ops) + blk_mq_request_bypass_insert(rq, false); + else + list_add_tail(&rq->queuelist, &q->queue_head); + return; + } + + /* + * @rq should go through flush machinery. Mark it part of flush + * sequence and submit for further processing. + */ + memset(&rq->flush, 0, sizeof(rq->flush)); + INIT_LIST_HEAD(&rq->flush.list); + rq->rq_flags |= RQF_FLUSH_SEQ; + rq->flush.saved_end_io = rq->end_io; /* Usually NULL */ + if (q->mq_ops) { + rq->end_io = mq_flush_data_end_io; + + spin_lock_irq(&fq->mq_flush_lock); + blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0); + spin_unlock_irq(&fq->mq_flush_lock); + return; + } + rq->end_io = flush_data_end_io; + + blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0); +} + +/** + * blkdev_issue_flush - queue a flush + * @bdev: blockdev to issue flush for + * @gfp_mask: memory allocation flags (for bio_alloc) + * @error_sector: error sector + * + * Description: + * Issue a flush for the block device in question. Caller can supply + * room for storing the error offset in case of a flush error, if they + * wish to. + */ +int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask, + sector_t *error_sector) +{ + struct request_queue *q; + struct bio *bio; + int ret = 0; + + if (bdev->bd_disk == NULL) + return -ENXIO; + + q = bdev_get_queue(bdev); + if (!q) + return -ENXIO; + + /* + * some block devices may not have their queue correctly set up here + * (e.g. loop device without a backing file) and so issuing a flush + * here will panic. Ensure there is a request function before issuing + * the flush. + */ + if (!q->make_request_fn) + return -ENXIO; + + bio = bio_alloc(gfp_mask, 0); + bio_set_dev(bio, bdev); + bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH; + + ret = submit_bio_wait(bio); + + /* + * The driver must store the error location in ->bi_sector, if + * it supports it. For non-stacked drivers, this should be + * copied from blk_rq_pos(rq). + */ + if (error_sector) + *error_sector = bio->bi_iter.bi_sector; + + bio_put(bio); + return ret; +} +EXPORT_SYMBOL(blkdev_issue_flush); + +struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q, + int node, int cmd_size, gfp_t flags) +{ + struct blk_flush_queue *fq; + int rq_sz = sizeof(struct request); + + fq = kzalloc_node(sizeof(*fq), flags, node); + if (!fq) + goto fail; + + if (q->mq_ops) + spin_lock_init(&fq->mq_flush_lock); + + rq_sz = round_up(rq_sz + cmd_size, cache_line_size()); + fq->flush_rq = kzalloc_node(rq_sz, flags, node); + if (!fq->flush_rq) + goto fail_rq; + + INIT_LIST_HEAD(&fq->flush_queue[0]); + INIT_LIST_HEAD(&fq->flush_queue[1]); + INIT_LIST_HEAD(&fq->flush_data_in_flight); + + return fq; + + fail_rq: + kfree(fq); + fail: + return NULL; +} + +void blk_free_flush_queue(struct blk_flush_queue *fq) +{ + /* bio based request queue hasn't flush queue */ + if (!fq) + return; + + kfree(fq->flush_rq); + kfree(fq); +} |